Ultracapacitors are widely used commercially at the present; the main application being energy storage for hybrid electric vehicles. Other applications, such as energy balancing in smart electrical grids, on-site energy storage for wind and solar energy projects, etc., are expected to materialize in the near future. The ultracapacitor was first described by Rightmire in 1966, in U.S. Pat. No. 3,288,641. For the past four decades, the basic structure of the ultracapacitor has hardly changed.
Fundamentally, an ultracapacitor consists of two metal plates separated by an insulator, just like an ordinary capacitor. The separator, however, is porous and is soaked in an electrolyte. Since ions that form in the electrolyte can move freely through the separator, positive and negative ions move in opposite directions and cling to their respective electrodes. The important feature in the ultracapacitor of the present invention is that the inner surface of each electrode is not a smooth surface but is rather padded with activated (porous) carbon. As with all terms used herein, the term“porous” is used with its common meaning of possessing or full of pores. This results in a surface area that is about 100,000 times as large as the surface area of an ordinary capacitor. The immense surface area of an ultracapacitor, however, is not the only important feature of the device. Since charges are carried by ions that cling to the inner surfaces of the electrodes, the practical distance between the positive and the negative charges at each electrode is on the order of a few nanometers (the size of a few molecules). As is well known, the capacitance of a parallel-plate capacitor is given by
  C  =                    ∈        0            ⁢              ∈        r            ⁢      A        d  
where ∈0 is the permittivity of free space, is the relative permittivity (or dielectric constant) of the dielectric present between the electrodes. A is the electrode area and d is the distance between the positive and the negative concentrations of charges. By maximizing A and minimizing d, therefore, ultracapacitors achieve extremely high values of capacitance. While the basic structure of the ultracapacitor has hardly changed since its introduction in 1966, some efforts and attempts to improve its performance include:    1. U.S. Pat. No. 6,059,847 by Farahmandi et al., which discloses a way for packaging the Rightmire ultracapacitor;    2. U.S. patent application Ser. No. 11/429,565 by Schindall et al., which discloses the concept of replacing the activated carbon by carbon nano-tubes, for the purpose of increasing the surface area A of the electrode. The general idea of such an approach, however, is not novel and has been shown in numerous earlier publications;    3. U.S. patent application Ser. No. 11/879,482 by Ehrenberg et al, which discloses a 3-layer capacitor structure. Two of the layers contain a polarizable polymer, and the third layer contains Barium Titanate. All three layers behave as independent capacitors and store energy in the polarizable medium. It is not obvious that such a structure will offer any advantages by comparison with the traditional ultracapacitor.    4. U.S. patent application Ser. No. 11/980,883 by Gadkaree et al., which discloses a modern chemical process for manufacturing the activated carbon in the Rightmire ultracapacitor.
With the ever increasing worldwide demand for energy, and the looming crises in petroleum supplies, energy storage, particularly for transportation applications, is emerging as an important area of research. As a result, the relatively new component known as an ultracapacitor or “super capacitor” has gained much attention recently. By comparison with batteries, ultracapacitors offer the advantages of very short charge/discharge time, virtually unlimited cycle life, zero maintenance requirements, and operability over a very wide range of temperatures. Ultracapacitors, however, still lag behind batteries in the aspect of energy density. The energy storage capability of commercially available ultracapacitors is about an order of magnitude lower than Lithium-ion batteries of the same dimensions, for example.
Thus, what is needed is an ultracapacitor that has a high energy density and that stores more energy than batteries, fuel cells and other technologies such that the ultracapacitor essentially equals the performance of gasoline. It, therefore, is an object of the invention to provide a very high density-energy ultracapacitor that greatly increases the energy density of an ultracapacitor, that is economical to build and efficient.